Date:   Fri, 4 Aug 2017 09:37:14 +0800
From:   Dou Liyang <douly.fnst@...fujitsu.com>
To:     Baoquan He <bhe@...hat.com>, Chao Fan <fanc.fnst@...fujitsu.com>
CC:     <linux-kernel@...r.kernel.org>, <x86@...nel.org>,
        <tglx@...utronix.de>, <mingo@...hat.com>, <hpa@...or.com>,
        <keescook@...omium.org>, <dyoung@...hat.com>, <arnd@...db.de>,
        <dave.jiang@...el.com>, <indou.takao@...fujitsu.com>,
        <izumi.taku@...fujitsu.com>
Subject: Re: [PATCH] x86/boot/KASLR: Extend movable_node option for KASLR

Hi Chao,Baoquan

At 08/04/2017 07:49 AM, Baoquan He wrote:
> On 08/03/17 at 08:24pm, Chao Fan wrote:
>> It's almost another "mem=".
>

No, it is different.

See Documentation/kernel-parameters:

"mem=" will force usage of a specific amount of memory and kernel will
not see the whole system memory.

But "movable_node=" will not do that.


> Then why not using 'mem=' directly?
>

Before answer this question, let's first discuss why the users want to
replace "mem=" with "movable_node" when they hope to support NUMA node
hot-plug.

I guess the real reason is that:

When booting up the system, We should have the whole memory not just
the un-hotpluggable memory which restrict by "mem=", eg:

we boot up kernel with 4 node:

node 0 size: 1024 MB  immovable
node 1 size: 1024 MB  movable
node 2 size: 1024 MB  movable
node 3 size: 1024 MB  movable

If we use "mem=1024M" in the command line, we just can use 1G memory.
But actually, we should have 4G normally.

Above is also one reason for why not using 'mem=' directly. Following
is other reasons:

1). each kernel option has its own role, we'd better misuse them.
2). movable_node is used as a boot-time switch to make nodes movable
or not, it should consider any situations, such as KASLR.


Thanks,
	dou.

>>
>> On Thu, Aug 03, 2017 at 08:17:21PM +0800, Dou Liyang wrote:
>>> movable_node is a boot-time switch to make hot-pluggable memory
>>> NUMA nodes to be movable. This option is based on an assumption
>>> that any node which the kernel resides in is defined as
>>> un-hotpluggable. Linux can allocates memory near the kernel image
>>> to try the best to keep the kernel away from hotpluggable memory
>>> in the same NUMA node. So other nodes can be movable.
>>>
>>> But, KASLR doesn't know which node is un-hotpluggable, the all
>>> hotpluggable memory ranges is recorded in ACPI SRAT table, SRAT
>>> is not parsed. So, KASLR may randomize the kernel in a movable
>>> node which will be immovable.
>>>
>>> Extend movable_node option to restrict kernel to be randomized in
>>> immovable nodes by adding a parameter. this parameter sets up
>>> the boundaries between the movable nodes and immovable nodes.
>>>
>>> Reported-by: Chao Fan <fanc.fnst@...fujitsu.com>
>>> Signed-off-by: Dou Liyang <douly.fnst@...fujitsu.com>
>>> ---
>>> Documentation/admin-guide/kernel-parameters.txt | 11 +++++++++--
>>> arch/x86/boot/compressed/kaslr.c                | 19 ++++++++++++++++---
>>> 2 files changed, 25 insertions(+), 5 deletions(-)
>>>
>>> diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
>>> index d9c171c..44c7e33 100644
>>> --- a/Documentation/admin-guide/kernel-parameters.txt
>>> +++ b/Documentation/admin-guide/kernel-parameters.txt
>>> @@ -2305,7 +2305,8 @@
>>> 	mousedev.yres=	[MOUSE] Vertical screen resolution, used for devices
>>> 			reporting absolute coordinates, such as tablets
>>>
>>> -	movablecore=nn[KMG]	[KNL,X86,IA-64,PPC] This parameter
>>> +	movablecore=nn[KMG]
>>> +			[KNL,X86,IA-64,PPC] This parameter
>>> 			is similar to kernelcore except it specifies the
>>> 			amount of memory used for migratable allocations.
>>> 			If both kernelcore and movablecore is specified,
>>> @@ -2315,12 +2316,18 @@
>>> 			that the amount of memory usable for all allocations
>>> 			is not too small.
>>>
>>> -	movable_node	[KNL] Boot-time switch to make hotplugable memory
>>> +	movable_node	[KNL] Boot-time switch to make hot-pluggable memory
>>> 			NUMA nodes to be movable. This means that the memory
>>> 			of such nodes will be usable only for movable
>>> 			allocations which rules out almost all kernel
>>> 			allocations. Use with caution!
>>>
>>> +	movable_node=nn[KMG]
>>> +			[KNL] Extend movable_node to work well with KASLR. This
>>> +			parameter is the boundaries between the movable nodes
>>> +			and immovable nodes, the memory which exceeds it will
>>> +			be regarded as hot-pluggable.
>>> +
>>> 	MTD_Partition=	[MTD]
>>> 			Format: <name>,<region-number>,<size>,<offset>
>>>
>>> diff --git a/arch/x86/boot/compressed/kaslr.c b/arch/x86/boot/compressed/kaslr.c
>>> index 91f27ab..7e2351b 100644
>>> --- a/arch/x86/boot/compressed/kaslr.c
>>> +++ b/arch/x86/boot/compressed/kaslr.c
>>> @@ -89,7 +89,10 @@ struct mem_vector {
>>> static bool memmap_too_large;
>>>
>>>
>>> -/* Store memory limit specified by "mem=nn[KMG]" or "memmap=nn[KMG]" */
>>> +/*
>>> + * Store memory limit specified by the following situations:
>>> + * "mem=nn[KMG]" or "memmap=nn[KMG]" or "movable_node=nn[KMG]"
>>> + */
>>> unsigned long long mem_limit = ULLONG_MAX;
>>>
>>>
>>> @@ -212,7 +215,8 @@ static int handle_mem_memmap(void)
>>> 	char *param, *val;
>>> 	u64 mem_size;
>>>
>>> -	if (!strstr(args, "memmap=") && !strstr(args, "mem="))
>>> +	if (!strstr(args, "memmap=") && !strstr(args, "mem=") &&
>>> +		!strstr(args, "movable_node="))
>>> 		return 0;
>>>
>>> 	tmp_cmdline = malloc(len + 1);
>>> @@ -247,7 +251,16 @@ static int handle_mem_memmap(void)
>>> 				free(tmp_cmdline);
>>> 				return -EINVAL;
>>> 			}
>>> -			mem_limit = mem_size;
>>> +			mem_limit = mem_limit > mem_size ? mem_size : mem_limit;
>>> +		} else if (!strcmp(param, "movable_node")) {
>>> +			char *p = val;
>>> +
>>> +			mem_size = memparse(p, &p);
>>> +			if (mem_size == 0) {
>>> +				free(tmp_cmdline);
>>> +				return -EINVAL;
>>> +			}
>>> +			mem_limit = mem_limit > mem_size ? mem_size : mem_limit;
>>> 		}
>>> 	}
>>>
>>> --
>>> 2.5.5
>>>
>>
>>
>
>
>

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